We tested whether aphid-induced changes in floral volatile production affects olfactory orientation by two important aphid natural enemies, both of which use aphid-induced volatiles in host location [23], [38] and can use flower resources as food. The experiments were designed to test the relative importance of volatile cues from flowering and vegetative plant parts, and comparative responses to plants infested with the different aphids species. Plants used as odour sources were enclosed in transparent polyester (PET) bags (Melitta Scandinavia, Sweden) (35×43 cm). For whole plant sources, a plant including its plastic pot and soil were enclosed in a bag sealed with a metal twist-tie above the soil. Where flower heads or green parts were separated, bags were sealed carefully around the stem using rubber foam and a twist-tie. A small hole was made through which a Teflon tube was inserted, sealed with labfilm (Parafilm) and connected to the olfactometer arm. A second hole was made in the opposite end of the bag with a Teflon tube connected through which air could enter and flow over the plant. The tube was 50 cm long to avoid re-collecting air in the direct vicinity of the odour sources. Aphid-damaged plants were infested with 200 aphids 72 h prior to the bioassays and aphids were not removed from the plant before the tests.